In an automatic analysis device for clinical test, certain amounts of sample and reagent are dispensed to induce reaction, and the absorbance of a reaction solution is measured for a certain time to obtain test values (concentrations or activity values) of a measurement target substance based on a measurement result. The test result plays an important role in various diagnoses by a doctor, such as figuring out medical conditions of a patient and determining effects of therapy. Therefore, accuracy control for ensuring correct measurement by the automatic analysis device is essential.
An example of a general accuracy management method includes a method of measuring an accuracy control sample with a known concentration and comparing the measurement result with a predetermined tolerance. The measurement and the comparison of the accuracy control sample are periodically executed between measurements of general (patient) specimens. If the measurement result of the accuracy control sample is within the tolerance, it can be determined that the measurement of the general specimens executed between the previous measurement of the accuracy control sample and the measurement this time is correctly executed.
An example of a method of ensuring the accuracy of the measurement of individual general specimens includes an accuracy management method using reaction process data (reaction process curve) (for example, see Patent Literature 1 and 2). The reaction process data denotes time-series data of the absorbance measured for a plurality of times after reaction of a reagent with a sample. The measurement method of clinical test is roughly divided into two types, an end-point method and a rate method, and the reaction process curve varies according to the methods.
The end-point method is used to measure concentrations of components, such as protein and fat mainly included in the sample. A substance generated by reaction of a component in the sample with a reagent becomes asymptotic to a certain amount with time, and the measurement value also becomes asymptotic to a certain value with time.
The rate method is mainly used to measure activities of enzyme components included in the sample, and instead of the concentration of an enzyme, an activity value of the enzyme is measured. A reagent and a certain amount of substrate are added to the sample to measure the activity value, and elements changed by consumption of the substrate by the enzyme are measured based on the reagent. The enzyme reaction rate is theoretically asymptotic to the upper limit if the substrate concentration is high on some level. A reagent for biochemical item measurement includes a sufficient amount of substrate. Therefore, if the reaction of the sample with the reagent is normal, the measurement value of the reaction in general linearly changes by certain amounts relative to the time change.
Patent Literature 1 and 2 illustrates methods of using an approximate equation derived based on a chemical reaction model to approximate a reaction process curve and comparing obtained approximate equation parameters and the like with a predetermined standard distribution of parameters (distribution of normal parameters or distribution of normal parameters and abnormal parameters). In the methods, if the approximate equation parameters and the like are included in a normal range, it is determined that the measurement is performed correctly. Patent Literature 1 describes an accuracy management method related to the end-point method, and Patent Literature 2 describes an accuracy management method related to the rate method.